1. Field of the Invention
This invention relates to an aerosol package of the well knwon type in which a valve is mounted at its upper end and has an actuator button. More specifically, this invention relates to such a package in which the propellant is a compressed gas which pressurizes the aerosol container during filling.
2. Description of Related Art including Information Disclosed under .sctn..sctn.1.97 to 1.99
In the past by far the dominant portion of aerosol packages have had as their propellant a liquid which has been mixed in with the aerosol product and which has had a comparatively low vapor pressure of about 30 psi. As the product has been propelled out with the aerosol discharge, the pressure has dropped and correspondingly more of the liquid propellant has gone into the vapor phase, renewing the presssure above the liquid and providing a propellant gas until the product has been used up.
The liquid propellant selected for use in most cases up until five years ago has been a chlorofluorocarbon (CFC). However, with environmental problems (including the deterioration of the ozone layer) government regulations have required that the use of such propellants be discontinued. Other propellants, such as butane, have been used but, of course, they are flammable and inappropriate in many applications.
Where the liquid product has been a food, such as whipped cream or cheese spread, the propellant has been in the form of compressed gas such as nitrogen or carbon dioxide. This has been satisfactory provided that the gas imposed on the containers has been under sufficient pressure to evacuate the entire package. Often to keep the gas and food products separate, the food has been disposed in a flexible bag within the aerosol container and the gas pressure has been imposed on the outside of the bag.
More recently, because of the environmental concern, the use of carbon dioxide, for instance, has been experimented with for insecticides and paints but it has been found that the spray patterns and other characteristics resulting from such aerosols have changed widely during the life of the package so that what at first has given a satisfactory spray pattern has produced an unacceptable spray pattern at the end of the package of vice versa.
Preferably, nitrous oxide or carbon dioxide has been used because they are somewhat soluble in most liquid products and, hence, have benefited the spray characteristics somewhat as they have come out of solution during discharge. Improved spray characteristics have been sought.
With liquid propellants such as CFC's it has been common to employ a vapor tap. A vapor tap, as is well known, is a passage which connects the gas above the liquid product in the container with the inside of the aerosol valve. Vapor taps have been used with such propellants to add to the liquid in the valve some of the vapor phase which acts to give a finer break-up, a lower delivery rate and a warmer spray. Vapor tap holes down to 0.005" have been made by laser equipment.
Insofar as I am aware, there have been no attempts to employ any kind of a vapor tap when working with compressed gas propellants. Such an arrangement has not been tried because one would expect that the gas, under relatively high pressure, would move directly and quickly through the vapor tap through the valve chamber and out the aerosol discharge, leaving the container with no propellant. Unlike with a liquid propellant, the compressed gas does not self-regulate between discharges, adding vapor phase when the pressure drops. Instead, when the pressure of the compressed gas drops, it does not "recover".